Vidicon grid consisting of set of parallel wires



Dec. 30, 1969 c p. KLOPPVING ET AL 3,487,250

VIDICON GRID CONSISTING OF SET OF PARALLEL WIRES Filed April 27, 1967 F|G.2 FIG.3

- H INVENTORS c REL P L PPIN wins QEESLACHG BY United States Patent US. Cl. 313-65 2 Claims ABSTRACT OF THE DISCLOSURE A Vidicon camera tube employs a fine-wire grid in stead of a mesh.

This invention relates to camera tubes of the Vidicon type, in which a fine-meshed electrode is arranged at a distance of a few millimeters from that side of the photosensitive screen which is adjacent the cathode."

Such a fine-meshed electrode arranged at the side of the cathode a few millimeters in front of the photosensitive screen serves to close the field of the lens electrodes and insures that the electron beam strikes the photosensitive screen as far as possible at right angles, even at the edges of the image. A fine-meshed gauze electrode is commonly used to obtain a uniform action in all directions.

This gauze must have a great fineness to avoid interfering images of the gauze in the picture. At the present time gauze is used having right-angled meshes with a pitch of approximately 34 microns, the metal parts between the meshes being from 5 microns to 6 microns wide. The gauze has a shadow ratio of approximately 1 to 4. Such fine gauze is manufactured by eledtjro-deposition of copper in a groove-provided glass plate. This method is very time-consuming and expensive; moreover, the glass plates with grooves can be manufactured only in very specialized work-places so that one fully depends upon them for the supply of such glass plates, and possibly also of the fine gauze. In spite of the advantage of the symmetrical action in all directions, the use of gauze for this electrode has, in addition to the above-mentioned disadvantage, the further disadvantage that the gauze as a whole may start vibrating so that microphony is likely to occur. Another disadvantage is that in certain color television systems, the frequency with which the electron beam passes through the crossings of the gauze may result in interference phenomena with the line frequency.

It is a principal object of the invention to provide a fine-mesh electrode for Vidicon camera tube which does not have the aforesaid disadvantages. This and further objects of the invention will appear as the specification progresses. I

According to the invention, as a fine-meshed electrode a grid consisting of parallel wires which have a thickness less than 10 microns and a pitch less than 50 microns, is employed instead of the gauze. The shadow ratio of the grid is greater than 1 to 3.

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Quite surprisingly, such a grid having a pitch less than 50 microns does not cause visible deformation of the electron spot on the screen. Also, the fact that the electrostatic field of the wires is not the same in all directions does not cause visible divergences for such a small pitch and thickness of wire. Against all expectations such grids do not cause microphony since in grids wound on a circular ring, not only the lengths of the wire are diiferent and hence their frequencies, but also it is found that the mechanical stresses in the wires are not the same. It is therefore also possible' to use grids secured to a rectangular frame, since despite the uniform length of the wires, the frequencies differ because of their different mechanical stresses.

In fact, the extremely thin wires of such a grid must be wound with a low tensile forceso that friction in the parts of the winding machine exerts a comparatively great influence on the mechanical stress of the wires.

Furthermore, the wires are soldered to the frame of the grid by heating. These causes appear to be responsible for the fact that the wires of the grid are not stretched uniformly so that microphony does not occur nor is the interference phenomena such as caused by the nodal points of a gauze grid. Furthermore, despite the use of special winding machines, the manufacture of such grids is much cheaper and less time consuming than the manufacture of known gauze grids.

The invention will now be described with reference to the accompanying drawing, in which FIG. 1 shows a Vidicon camera tube according to the invention, and

FIG. 2 and 3 show different grids for such a tube according to the invention.

The Vidicon tube of FIGURE 1 comprises an envelope 1 in which a photosensitive layer 2 is provided on the inner side of a window 3. The tube also contains an electron lens 6. A grid electrode 4 according to the invention which is supported by a ring 5, is arranged in the tube at a distance less than 2 mms. from the screen 2.

Parallel wires 4 are wound on the ring 5, as shown in FIGURE 2, and secured thereto with the use of solder (not shown). The thickness of the wire is 5 microns and the pitch is 30 microns so that the shadow ratio is 1 to 5. The electron spot on the screen 2 in such a tube is between 30 microns and 60 microns in diameter and hence of the same order of magnitude as the pitch of the grid.

In FIGURE 3 the grid wire 8 is wound on a rectangular frame 7 and soldered thereto. The frame 7 is supported by a frame 9 fitted in the tube 1.

Although only two embodiments have been described, a grid can also be manufactured or formed in a different manner. The thickness of the wire used is between 3 microns and 8 microns and the pitch is between 30 microns and 50 microns.

The tube will generally be assembled so that the direction of the image lines is approximately at right angles tothe direction of the grid wires.

While the invention has been described with reference to specific embodiments and applications thereof, other modifications will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention which is defined in the appended claims.

What is claimed is:

1. A camera tube of the Vidicon type comprising an evacuated envelope, and within the envelope an electron beam source, a photosensitive screen spaced from the beam source, means to scan the screen with said beam, and a fine-meshed electrode spaced a few millimeters from that side of the photosensitive screen which faces said beam source, said fine-meshed electrode consisting of a set of parallel wires approximately at right angles to the image lines, said wires each having a thickness less than 10 microns and a pitch less than 50 microns, the shadow ratio of the grid being greater than 1 to 3.

2. A camera tube as claimed in claim 1, in which said fine-meshed electrode surface is rectangular.

References Cited UNITED STATES PATENTS 7/1958 Wardley. 8/1958 Borkan 313-348 X 4/ 1959 Ehrenhaft et al. 7/1959 Salgo.

US. Cl. X.R. 

